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'\"
'\" Copyright (c) 1996-1997 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
'\" SCCS: @(#) OpenFileChnl.3 1.39 97/05/09 18:14:49
.so man.macros
.TH Tcl_OpenFileChannel 3 8.0 Tcl "Tcl Library Procedures"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
Tcl_OpenFileChannel, Tcl_OpenCommandChannel, Tcl_MakeFileChannel, Tcl_GetChannel, Tcl_RegisterChannel, Tcl_UnregisterChannel, Tcl_Close, Tcl_Read, Tcl_Gets, Tcl_Write, Tcl_Flush, Tcl_Seek, Tcl_Tell, Tcl_Eof, Tcl_InputBlocked, Tcl_InputBuffered, Tcl_GetChannelOption, Tcl_SetChannelOption \- buffered I/O facilities using channels
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
typedef ... Tcl_Channel;
.sp
Tcl_Channel
\fBTcl_OpenFileChannel\fR(\fIinterp, fileName, mode, permissions\fR)
.sp
Tcl_Channel
\fBTcl_OpenCommandChannel\fR(\fIinterp, argc, argv, flags\fR)
.VS
.sp
Tcl_Channel
\fBTcl_MakeFileChannel\fR(\fIhandle, readOrWrite\fR)
.VE
.sp
Tcl_Channel
\fBTcl_GetChannel\fR(\fIinterp, channelName, modePtr\fR)
.sp
void
\fBTcl_RegisterChannel\fR(\fIinterp, channel\fR)
.sp
int
\fBTcl_UnregisterChannel\fR(\fIinterp, channel\fR)
.sp
int
\fBTcl_Close\fR(\fIinterp, channel\fR)
.sp
int
\fBTcl_Read\fR(\fIchannel, buf, toRead\fR)
.sp
int
\fBTcl_Gets\fR(\fIchannel, lineRead\fR)
.sp
int
\fBTcl_GetsObj\fR(\fIchannel, lineObjPtr\fR)
.sp
int
\fBTcl_Write\fR(\fIchannel, buf, toWrite\fR)
.sp
int
\fBTcl_Flush\fR(\fIchannel\fR)
.sp
int
\fBTcl_Seek\fR(\fIchannel, offset, seekMode\fR)
.sp
int
\fBTcl_Tell\fR(\fIchannel\fR)
.sp
int
\fBTcl_GetChannelOption\fR(\fIchannel, optionName, optionValue\fR)
.sp
int
\fBTcl_SetChannelOption\fR(\fIinterp, channel, optionName, newValue\fR)
.sp
int
\fBTcl_Eof\fR(\fIchannel\fR)
.sp
int
\fBTcl_InputBlocked\fR(\fIchannel\fR)
.sp
int
\fBTcl_InputBuffered\fR(\fIchannel\fR)
.sp
.SH ARGUMENTS
.AS Tcl_ChannelType newClientProcPtr in
.AP Tcl_Interp *interp in
Used for error reporting and to look up a channel registered in it.
.AP char *fileName in
The name of a local or network file.
.AP char *mode in
Specifies how the file is to be accessed.  May have any of the
values allowed for the \fImode\fR argument to the Tcl
\fBopen\fR command.
For \fBTcl_OpenCommandChannel\fR, may be NULL.
.AP int permissions in
POSIX-style permission flags such as 0644.
If a new file is created, these permissions will be set on the
created file.
.AP int argc in
The number of elements in \fIargv\fR.
.AP char **argv in
Arguments for constructing a command pipeline.
These values have the same meaning as the non-switch arguments
to the Tcl \fBexec\fR command.
.AP int flags in
Specifies the disposition of the stdio handles in pipeline: OR-ed
combination of \fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, \fBTCL_STDERR\fR,
and \fBTCL_ENFORCE_MODE\fR. If \fBTCL_STDIN\fR is set, stdin for
the first child in the pipe is the pipe channel, otherwise it is the same
as the standard input of the invoking process; likewise for
\fBTCL_STDOUT\fR and \fBTCL_STDERR\fR. If \fBTCL_ENFORCE_MODE\fR is not set,
then the pipe can redirect stdio handles to override the stdio handles for
which \fBTCL_STDIN\fR, \fBTCL_STDOUT\fR and \fBTCL_STDERR\fR have been set.
If it is set, then such redirections cause an error.
.VS
.AP ClientData handle in
Operating system specific handle for I/O to a file. For Unix this is a
file descriptor, for Windows it is a HANDLE.
.AP int readOrWrite in
OR-ed combination of \fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR to indicate
what operations are valid on \fIhandle\fR.
.VE
.AP int *modePtr out
Points at an integer variable that will receive an OR-ed combination of
\fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR denoting whether the channel is
open for reading and writing.
.AP Tcl_Channel channel in
A Tcl channel for input or output.  Must have been the return value
from a procedure such as \fBTcl_OpenFileChannel\fR.
.AP char *buf in
An array of bytes in which to store channel input, or from which
to read channel output.
.AP int len in
The length of the input or output.
.AP int atEnd in
If nonzero, store the input at the end of the input queue, otherwise store
it at the head of the input queue.
.AP int toRead in
The number of bytes to read from the channel.
.AP Tcl_DString *lineRead in
A pointer to a Tcl dynamic string in which to store the line read from the
channel.  Must have been initialized by the caller.  The line read
will be appended to any data already in the dynamic string.
.AP Tcl_Obj *linePtrObj in
A pointer to a Tcl object in which to store the line read from the
channel.  The line read will be appended to the current value of the
object. 
.AP int toWrite in
The number of bytes to read from \fIbuf\fR and output to the channel.
.AP int offset in
How far to move the access point in the channel at which the next input or
output operation will be applied, measured in bytes from the position
given by \fIseekMode\fR.  May be either positive or negative.
.AP int seekMode in
Relative to which point to seek; used with \fIoffset\fR to calculate the new
access point for the channel. Legal values are \fBSEEK_SET\fR,
\fBSEEK_CUR\fR, and \fBSEEK_END\fR.
.AP char *optionName in
The name of an option applicable to this channel, such as \fB\-blocking\fR.
May have any of the values accepted by the \fBfconfigure\fR command.
.AP Tcl_DString *optionValue in
Where to store the value of an option or a list of all options and their
values. Must have been initialized by the caller.
.AP char *newValue in
New value for the option given by \fIoptionName\fR.
.BE

.SH DESCRIPTION
.PP
The Tcl channel mechanism provides a device-independent and
platform-independent mechanism for performing buffered input
and output operations on a variety of file, socket, and device
types.
The channel mechanism is extensible to new channel types, by
providing a low level channel driver for the new type; the channel driver
interface is described in the manual entry for \fBTcl_CreateChannel\fR. The
channel mechanism provides a buffering scheme modelled after
Unix's standard I/O, and it also allows for nonblocking I/O on
channels.
.PP
The procedures described in this manual entry comprise the C APIs of the
generic layer of the channel architecture. For a description of the channel
driver architecture and how to implement channel drivers for new types of
channels, see the manual entry for \fBTcl_CreateChannel\fR.

.SH TCL_OPENFILECHANNEL
.PP
\fBTcl_OpenFileChannel\fR opens a file specified by \fIfileName\fR and
returns a channel handle that can be used to perform input and output on
the file. This API is modelled after the \fBfopen\fR procedure of
the Unix standard I/O library.
The syntax and meaning of all arguments is similar to those
given in the Tcl \fBopen\fR command when opening a file.
If an error occurs while opening the channel, \fBTcl_OpenFileChannel\fR
returns NULL and records a POSIX error code that can be
retrieved with \fBTcl_GetErrno\fR.
In addition, if \fIinterp\fR is non-NULL, \fBTcl_OpenFileChannel\fR
leaves an error message in \fIinterp->result\fR after any error.
.PP
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR, described below.
If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.

.SH TCL_OPENCOMMANDCHANNEL
.PP
\fBTcl_OpenCommandChannel\fR provides a C-level interface to the
functions of the \fBexec\fR and \fBopen\fR commands.
It creates a sequence of subprocesses specified
by the \fIargv\fR and \fIargc\fR arguments and returns a channel that can
be used to communicate with these subprocesses.
The \fIflags\fR argument indicates what sort of communication will
exist with the command pipeline.
.PP
If the \fBTCL_STDIN\fR flag is set then the standard input for the
first subprocess will be tied to the channel: writing to the channel
will provide input to the subprocess.  If \fBTCL_STDIN\fR is not set,
then standard input for the first subprocess will be the same as this
application's standard input.  If \fBTCL_STDOUT\fR is set then
standard output from the last subprocess can be read from the channel;
otherwise it goes to this application's standard output.  If
\fBTCL_STDERR\fR is set, standard error output for all subprocesses is
returned to the channel and results in an error when the channel is
closed; otherwise it goes to this application's standard error.  If
\fBTCL_ENFORCE_MODE\fR is not set, then \fIargc\fR and \fIargv\fR can
redirect the stdio handles to override \fBTCL_STDIN\fR,
\fBTCL_STDOUT\fR, and \fBTCL_STDERR\fR; if it is set, then it is an
error for argc and argv to override stdio channels for which
\fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, and \fBTCL_STDERR\fR have been set.
.PP
If an error occurs while opening the channel, \fBTcl_OpenCommandChannel\fR
returns NULL and records a POSIX error code that can be retrieved with
\fBTcl_GetErrno\fR.
In addition, \fBTcl_OpenCommandChannel\fR leaves an error message in
\fIinterp->result\fR if \fIinterp\fR is not NULL.
.PP
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR, described below.
If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.

.SH TCL_MAKEFILECHANNEL
.PP
\fBTcl_MakeFileChannel\fR makes a \fBTcl_Channel\fR from an existing,
platform-specific, file handle.
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR, described below.
If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.

.SH TCL_GETCHANNEL
.PP
\fBTcl_GetChannel\fR returns a channel given the \fIchannelName\fR used to
create it with \fBTcl_CreateChannel\fR and a pointer to a Tcl interpreter in
\fIinterp\fR. If a channel by that name is not registered in that interpreter,
the procedure returns NULL. If the \fImode\fR argument is not NULL, it
points at an integer variable that will receive an OR-ed combination of
\fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR describing whether the channel is
open for reading and writing.

.SH TCL_REGISTERCHANNEL
.PP
\fBTcl_RegisterChannel\fR adds a channel to the set of channels accessible
in \fIinterp\fR. After this call, Tcl programs executing in that
interpreter can refer to the channel in input or output operations using
the name given in the call to \fBTcl_CreateChannel\fR.  After this call,
the channel becomes the property of the interpreter, and the caller should
not call \fBTcl_Close\fR for the channel; the channel will be closed
automatically when it is unregistered from the interpreter.
.PP
Code executing outside of any Tcl interpreter can call
\fBTcl_RegisterChannel\fR with \fIinterp\fR as NULL, to indicate that it
wishes to hold a reference to this channel. Subsequently, the channel can
be registered in a Tcl interpreter and it will only be closed when the
matching number of calls to \fBTcl_UnregisterChannel\fR have been made.
This allows code executing outside of any interpreter to safely hold a
reference to a channel that is also registered in a Tcl interpreter.

.SH TCL_UNREGISTERCHANNEL
.PP
\fBTcl_UnregisterChannel\fR removes a channel from the set of channels
accessible in \fIinterp\fR. After this call, Tcl programs will no longer be
able to use the channel's name to refer to the channel in that interpreter.
If this operation removed the last registration of the channel in any
interpreter, the channel is also closed and destroyed.
.PP
Code not associated with a Tcl interpreter can call
\fBTcl_UnregisterChannel\fR with \fIinterp\fR as NULL, to indicate to Tcl
that it no longer holds a reference to that channel. If this is the last
reference to the channel, it will now be closed.

.SH TCL_CLOSE
.PP
\fBTcl_Close\fR destroys the channel \fIchannel\fR, which must denote a
currently open channel. The channel should not be registered in any
interpreter when \fBTcl_Close\fR is called. Buffered output is flushed to
the channel's output device prior to destroying the channel, and any
buffered input is discarded.  If this is a blocking channel, the call does
not return until all buffered data is successfully sent to the channel's
output device.  If this is a nonblocking channel and there is buffered
output that cannot be written without blocking, the call returns
immediately; output is flushed in the background and the channel will be
closed once all of the buffered data has been output.  In this case errors
during flushing are not reported.
.PP
If the channel was closed successfully, \fBTcl_Close\fR returns \fBTCL_OK\fR.
If an error occurs, \fBTcl_Close\fR returns \fBTCL_ERROR\fR and records a
POSIX error code that can be retrieved with \fBTcl_GetErrno\fR.
If the channel is being closed synchronously and an error occurs during
closing of the channel and \fIinterp\fR is not NULL, an error message is
left in \fIinterp->result\fR.
.PP
Note: it is not safe to call \fBTcl_Close\fR on a channel that has been
registered using \fBTcl_RegisterChannel\fR; see the documentation for
\fBTcl_RegisterChannel\fR, above, for details. If the channel has ever been
given as the \fBchan\fR argument in a call to \fBTcl_RegisterChannel\fR,
you should instead use \fBTcl_UnregisterChannel\fR, which will internally
call \fBTcl_Close\fR when all calls to \fBTcl_RegisterChannel\fR have been
matched by corresponding calls to \fBTcl_UnregisterChannel\fR.

.SH TCL_READ
.PP
\fBTcl_Read\fR consumes up to \fItoRead\fR bytes of data from
\fIchannel\fR and stores it at \fIbuf\fR.
The return value of \fBTcl_Read\fR is the number of characters written
at \fIbuf\fR.
The buffer produced by \fBTcl_Read\fR is not NULL terminated. Its contents
are valid from the zeroth position up to and excluding the position
indicated by the return value.
If an error occurs, the return value is -1 and \fBTcl_Read\fR records
a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR.
.PP
The return value may be smaller than the value of \fItoRead\fR, indicating
that less data than requested was available, also called a \fIshort
read\fR.
In blocking mode, this can only happen on an end-of-file.
In nonblocking mode, a short read can also occur if there is not
enough input currently available:  \fBTcl_Read\fR returns a short
count rather than waiting for more data.
.PP
If the channel is in blocking mode, a return value of zero indicates an end
of file condition. If the channel is in nonblocking mode, a return value of
zero indicates either that no input is currently available or an end of
file condition. Use \fBTcl_Eof\fR and \fBTcl_InputBlocked\fR
to tell which of these conditions actually occurred.
.PP
\fBTcl_Read\fR translates platform-specific end-of-line representations
into the canonical \fB\en\fR internal representation according to the
current end-of-line recognition mode. End-of-line recognition and the
various platform-specific modes are described in the manual entry for the
Tcl \fBfconfigure\fR command.

.SH TCL_GETS AND TCL_GETSOBJ
.PP
\fBTcl_Gets\fR reads a line of input from a channel and appends all of
the characters of the line except for the terminating end-of-line character(s)
to the dynamic string given by \fIdsPtr\fR.
The end-of-line character(s) are read and discarded.
.PP
If a line was successfully read, the return value is greater than or
equal to zero, and it indicates the number of characters stored
in the dynamic string.
If an error occurs, \fBTcl_Gets\fR returns -1 and records a POSIX error
code that can be retrieved with \fBTcl_GetErrno\fR.
\fBTcl_Gets\fR also returns -1 if the end of the file is reached;
the \fBTcl_Eof\fR procedure can be used to distinguish an error
from an end-of-file condition.
.PP
If the channel is in nonblocking mode, the return value can also
be -1 if no data was available or the data that was available
did not contain an end-of-line character.
When -1 is returned, the \fBTcl_InputBlocked\fR procedure may be
invoked to determine if the channel is blocked because of input
unavailability.
.PP
\fBTcl_GetsObj\fR is the same as \fBTcl_Gets\fR except the resulting
characters are appended to a Tcl object \fBlineObjPtr\fR rather than a
dynamic string.
.SH TCL_WRITE
.PP
\fBTcl_Write\fR accepts \fItoWrite\fR bytes of data at \fIbuf\fR for output
on \fIchannel\fR. This data may not appear on the output device
immediately. If the data should appear immediately, call \fBTcl_Flush\fR
after the call to \fBTcl_Write\fR, or set the \fB-buffering\fR option on
the channel to \fBnone\fR. If you wish the data to appear as soon as an end
of line is accepted for output, set the \fB\-buffering\fR option on the
channel to \fBline\fR mode.
.PP
The \fItoWrite\fR argument specifies how many bytes of data are provided in
the \fIbuf\fR argument. If it is negative, \fBTcl_Write\fR expects the data
to be NULL terminated and it outputs everything up to the NULL.
.PP
The return value of \fBTcl_Write\fR is a count of how many
characters were accepted for output to the channel. This is either equal to
\fItoWrite\fR or -1 to indicate that an error occurred.
If an error occurs, \fBTcl_Write\fR also records a POSIX error code
that may be retrieved with \fBTcl_GetErrno\fR.
.PP
Newline characters in the output data are translated to platform-specific
end-of-line sequences according to the \fB\-translation\fR option for
the channel.

.SH TCL_FLUSH
.PP
\fBTcl_Flush\fR causes all of the buffered output data for \fIchannel\fR
to be written to its underlying file or device as soon as possible.
If the channel is in blocking mode, the call does not return until
all the buffered data has been sent to the channel or some error occurred.
The call returns immediately if the channel is nonblocking; it starts
a background flush that will write the buffered data to the channel
eventually, as fast as the channel is able to absorb it.
.PP
The return value is normally \fBTCL_OK\fR.
If an error occurs, \fBTcl_Flush\fR returns \fBTCL_ERROR\fR and
records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR.

.SH TCL_SEEK
.PP
\fBTcl_Seek\fR moves the access point in \fIchannel\fR where subsequent
data will be read or written. Buffered output is flushed to the channel and
buffered input is discarded, prior to the seek operation.
.PP
\fBTcl_Seek\fR normally returns the new access point.
If an error occurs, \fBTcl_Seek\fR returns -1 and records a POSIX error
code that can be retrieved with \fBTcl_GetErrno\fR.
After an error, the access point may or may not have been moved.

.SH TCL_TELL
.PP
\fBTcl_Tell\fR returns the current access point for a channel. The returned
value is -1 if the channel does not support seeking.

.SH TCL_GETCHANNELOPTION
.PP
\fBTcl_GetChannelOption\fR retrieves, in \fIdsPtr\fR, the value of one of
the options currently in effect for a channel, or a list of all options and
their values.  The \fIchannel\fR argument identifies the channel for which
to query an option or retrieve all options and their values.
If \fIoptionName\fR is not NULL, it is the name of the
option to query; the option's value is copied to the Tcl dynamic string
denoted by \fIoptionValue\fR. If
\fIoptionName\fR is NULL, the function stores an alternating list of option
names and their values in \fIoptionValue\fR, using a series of calls to
\fBTcl_DStringAppendElement\fR. The various preexisting options and
their possible values are described in the manual entry for the Tcl
\fBfconfigure\fR command. Other options can be added by each channel type.
These channel type specific options are described in the manual entry for
the Tcl command that creates a channel of that type; for example, the
additional options for TCP based channels are described in the manual entry
for the Tcl \fBsocket\fR command.
The procedure normally returns \fBTCL_OK\fR. If an error occurs, it returns
\fBTCL_ERROR\fR and calls \fBTcl_SetErrno\fR to store an appropriate POSIX
error code.

.SH TCL_SETCHANNELOPTION
.PP
\fBTcl_SetChannelOption\fR sets a new value for an option on \fIchannel\fR.
\fIOptionName\fR is the option to set and \fInewValue\fR is the value to
set.
The procedure normally returns \fBTCL_OK\fR.  If an error occurs,
it returns \fBTCL_ERROR\fR;  in addition, if \fIinterp\fR is non-NULL,
\fBTcl_SetChannelOption\fR leaves an error message in \fIinterp->result\fR.

.SH TCL_EOF
.PP
\fBTcl_Eof\fR returns a nonzero value if \fIchannel\fR encountered
an end of file during the last input operation.

.SH TCL_INPUTBLOCKED
.PP
\fBTcl_InputBlocked\fR returns a nonzero value if \fIchannel\fR is in
nonblocking mode and the last input operation returned less data than
requested because there was insufficient data available.
The call always returns zero if the channel is in blocking mode.

.SH TCL_INPUTBUFFERED
.PP
\fBTcl_InputBuffered\fR returns the number of bytes of input currently
buffered in the internal buffers for a channel. If the channel is not open
for reading, this function always returns zero.

.VS
.SH "PLATFORM ISSUES"
.PP
The handles returned from \fBTcl_GetChannelHandle\fR depend on the
platform and the channel type.  On Unix platforms, the handle is
always a Unix file descriptor as returned from the \fBopen\fR system
call.  On Windows platforms, the handle is a file \fBHANDLE\fR when
the channel was created with \fBTcl_OpenFileChannel\fR,
\fBTcl_OpenCommandChannel\fR, or \fBTcl_MakeFileChannel\fR.  Other
channel types may return a different type of handle on Windows
platforms.  On the Macintosh platform, the handle is a file reference
number as returned from \fBHOpenDF\fR.
.VE

.SH "SEE ALSO"
DString(3), fconfigure(n), filename(n), fopen(2), Tcl_CreateChannel(3)

.SH KEYWORDS
access point, blocking, buffered I/O, channel, channel driver, end of file,
flush, input, nonblocking, output, read, seek, write